The present invention relates to a single-chip micro-computer and particularly relates to memory access signal terminals of such a micro-computer.
Conventional single-chip micro-computers output memory address signals to the outside through exclusively-used or private terminals therefor. Therefore, the terminals for memory address signals are exclusively used for controlling external memories. For example, in a system in which a keyboard is constituted by combining input terminals and output terminals in the form of a matrix, output terminals other than the memory address signal terminals are provided to be used for a key matrix.
This type single-chip micro-computer, however, requires a larger number of signal terminals as the storage capacity of the external memory increases. In particular, in the case where the single-chip micro-computer is used in an electronic memorandum book, an electronic dictionary, or the like, the number of terminals in an IC increases remarkably for the following reasons.
1) Large-capacity memory devices such as RAMs, ROMs and the like are connected externally, so that a large number of memory address signals, a large number of data input-output signals and a large number of control signals for reading, writing and the like are required. PA0 2) There are many cases where a large-capacity liquid crystal display panel for dot matrix display or the like is used, so that a large number of liquid crystal driving terminals are required when a liquid crystal driving circuit is incorporated in the single-chip micro-computer. Specifically, even in the case where 24 characters of 5.times.7 dot matrix are displayed with a 1/16 duty factor, 76 terminals are required as the sum of 16 common terminals and 60 segment terminals. PA0 3) It is general that a keyboard is used in the operation of the electronic memorandum book or the electronic dictionary, so that input terminals and output terminals are required for forming a key matrix.
When this type conventional single-chip micro-computer is applied to the aforementioned field, a very large number of terminals are required as described above. Therefore, a fine-pitch multi-pin package is required or a large chip size of the single-chip micro-computer is required. As a result, this type single-chip micro-computer becomes expensive. Further, the number of wirings in a substrate for mounting the single-chip micro-computer increases, so that mounting a fine-pitch IC package is required.. Therefore, a mounting technique of higher order is required. As a result, not only the IC but finished products become expensive.